Typing hooks

useState and useRef infer their types from the initial value, so you only spell one out when the initial value does not show the full type: null before data arrives, or an empty array.

What a session covers

The tutor works through these with you, in conversation and code. A session ends when you have shown them, not when a video does.

Explain when useState infers the type and when it needs a type argument
Write useState for a value that starts as null and arrives later
Spot the useState(null) that stays null forever

In practice

A few lines that show Typing hooks doing its job.

TSX

const [user, setUser] = useState<User | null>(null);
const [tags, setTags] = useState<string[]>([]);
const inputRef = useRef<HTMLInputElement>(null);

function useToggle(initial = false): [boolean, () => void] {
  const [on, setOn] = useState(initial);
  return [on, () => setOn((v) => !v)];
}

The common mistake

Watch for

Writing useState(null) with no type argument. The state is typed as null forever, and setUser(data) is a compile error.

What to know first

Your roadmap puts these before Typing hooks, unless you already know them.

How it stays learned

Once a session shows you understand Typing hooks, it comes back for review. Each review takes a minute and tells the memory model how well you still know it.

Day 3First recall, while it is fresh
Day 7Second, a week on
Day 18Last, when it has settled

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